Re: [net-next RFC V5 4/5] virtio_net: multiqueue support

[Jason Wang]

On 07/29/2012 05:44 PM, Michael S. Tsirkin wrote:
> On Sat, Jul 21, 2012 at 02:02:58PM +0200, Sasha Levin wrote:
> > On 07/20/2012 03:40 PM, Michael S. Tsirkin wrote:
> > > > -	err = init_vqs(vi);
> > > > > +	if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ))
> > > > > +		vi->has_cvq = true;
> > > > > +
> > > How about we disable multiqueue if there's no cvq?
> > > Will make logic a bit simpler, won't it?
> > multiqueues don't really depend on cvq. Does this added complexity really justifies adding an artificial limit?
> Well !cvq support is a legacy feature: the reason we support it
> in driver is to avoid breaking on old hosts. Adding more code to that
> path just doesn't make much sense since old hosts won't have mq.

After some thought about this, maybe there's no need to the cvq for the 
negotiation if we want support only two modes ( 1 tx/rx queue pair and N 
tx/rx queue pairs). We can do this just through the feature bit negotiation.
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